1. Field of the Invention
Embodiments of the invention generally relate to electrochemical plating and, more particularly, to a contact ring for an electrochemical plating system.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio (greater than about 4:1, for example) interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as the interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as promising processes for void free filling of sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate (or a layer deposited thereon) may be efficiently filled with a conductive material, such as copper, for example. An ECP processes generally includes first depositing a seed layer over the surface and into features of the substrate (the seed layer deposition process is generally separate from the ECP plating process), and then the surface features of the substrate are exposed to an electrochemical plating solution, while an electrical bias is simultaneously applied between the substrate and an anode positioned in the plating solution. The plating solution is generally rich in positive ions to be plated onto the surface of the substrate, and therefore, the application of the electrical bias causes these positive ions to be urged out of the plating solution and to be plated onto the seed layer.
Typically, the electrical bias is provided to the substrate via one or more electrical contacts distributed around the perimeter of the substrate being plated. Commonly, the seed layer formed on the substrate may extend from a plating surface around beveled edges of the substrate, and possibly extend onto a non-plating surface or backside of the substrate. Accordingly, for different systems, the electrical contacts may be in electrical contact with either the plating surface (frontside) or the non-plating surface (backside) of the substrate. Regardless of location, it is generally desirable to isolate the electrical contacts, as well as the non-plating surface of the substrate from the plating material in order to avoid plating of the positive ions on the contacts, as plating on the electrical contacts may alter the resistance of the electrical contacts and have a negative effect on the substrate plating uniformity.
Conventional approaches to isolate the electrical contacts and non-plating surface from the plating solution typically include providing one or more sealing elements to contact the same surface of the substrate as the electrical contacts. For example, sealing members positioned to engage the plating surface may be placed adjacent electrical contacts positioned to contact the plating surface. The sealing members and electrical contacts also provide support for the substrate. However, the combination of the electrical contacts and the associated seals generally takes up several millimeters (generally between 3 and about 7 millimeters) of the perimeter of the plating surface area. Since this surface area is used to make electrical and seal contacts, the area cannot be used to support device formation.
In an effort to utilize this perimeter surface area, some systems may include sealing members positioned to engage the non-plating surface adjacent electrical contacts positioned to contact the non-plating surface. However, without sealing members or electrical contacts on the plating surface to support the substrate, some other means may be needed to support the substrate. Typically, a vacuum is applied to the substrate, to pull the non-plating surface up into contact with the sealing members and electrical contacts. However, the vacuum applied to the substrate may create a stress on the substrate, and may lead to substrate breakage. If the sealing members happen to leak, the vacuum may be unable to maintain the substrate against the electrical contacts with sufficient force and the plating solution may enter the vacuum, causing damage to the vacuum. Further, in systems where the contact pins engage the plating surface of the substrate, the contact pins are generally surrounded by a seal configured to prevent the electroplating solution from coming into contact with the electrical contact pins. Although the concept of dry contact pins is noteworthy, there are several disadvantages of these configurations. Namely, dry contact configurations present challenges in maintaining a fluid tight seal between the substrate, and as such, fluid often penetrates the seals and is exposed to the contact pins, which alters the pin resistance and the plating uniformity. Additionally, conventional contact rings utilize fixed electrical contacts, and therefore, when a substrate being plated is not entirely planar, the various fixed contacts will have varying degrees of success contacting the substrate.
Therefore, there is a need for an improved apparatus for securing a substrate in an electrochemical plating system.